The present invention relates to tube and fin heat exchangers, such as condensers in refrigerator or air conditioning units.
In producing a heat transfer surface, it is economically advantageous to attempt to provide the exposed surface area in contact with two fluids in an inverse ratio of the fluid s ability to transfer heat. For example, in a refrigerant to air exchanger, refrigerant has a significantly greater ability to transfer heat to the inside of its tubular container than does air to the outside of the tubing. For this reason, it is accepted practice to add surface area to the air side of the device in the form of fins. The present invention employs a unique fabricating process to improve fin material utilization and increase the heat transfer coefficient by miniaturizing fins into small strips.
It is well known by those skilled in heat transfer that the air side heat transfer coefficient is enhanced almost asymptotically with the inverse of fin perimeter, particularly when the fins members are arranged in a position perpendicular to the direction of air flow. This maximizes the flow of heat between fin and air by minimizing the boundary layer of stagnant air at the fin surface.
In simplistic form the equation for transfer of heat is Q=Ah.DELTA.T, where Q is the heat transfered in BTU/hr, A is the surface area, h is the film heat transfer coefficient, and .DELTA.T is the difference in temperature. The heat transfer coefficient h between the refrigerant and the tube is very high (about 200 to 300 BTU/hr/Deg F.), while the h for air is quite low (from 8 to 30 BTU/hr/Deg/F.). From a practical standpoint it is never possible to apply sufficient external surface area to overcome this difference in heat transfer coefficient for the two fluids. However, the value of air side heat transfer coefficient can be enhanced significantly by producing the fins in the form of strips with minimum distance from the leading edge to the leaving edge. Thus, increasing the heat transfer coefficient and reducing fin width minimizes boundary layer depth, providing increased air side heat transfer.